Small power tools (including pneumatic or electric ones) are well accepted on the market due to their smaller size and lower prices and energy consumption. The power tools include a wide variety of types, such as emery wheel machines, drilling machines, pneumatic (or electric) wrenches and the like. Some of the power tools aim for drilling, sanding or grinding, and a great amount of dust is produced in the working places during operation. It is hazardous to the health of workers. Hence a lot of improved structures are developed for power tools to solve the dust scattering problem. For instance, R.O.C. patent No. M349818 entitled “Improved grinding machine” provides a casing and a handgrip at one side. The handgrip has an input portion (121) and an output portion (122). The input portion receives electric power or high pressure air needed for operation. The output portion aims to discharge dust, impurities and mist generated on the surface of working pieces during sanding or grinding operation. Referring to the specification and FIG. 5 of aforesaid reference, the output portion is an air discharge duct to inhale airflow and discharge waste such as dust and the like. It provides some improvements on the dust scattering problem. Similar structures of power tools can be found in R.O.C. patent Nos. M245007, I260255 and 493485.
While the aforesaid references provide dust inhalation function, they have a common drawback. Take R.O.C. patent No. M349818 as an example, in its FIG. 5, the air discharge duct has an opening formed on a hood surrounding a grinding pad (3), and the opening is connected to the output portion (122), i.e. the air discharge duct. Then the air discharge duct is connected to an inhalation device to generate suction in the output portion to inhale the dust and impurities into the output portion. The suction is stronger at the front side of the opening due to its shape and location, but deceases significantly after deviating slightly from the opening. Moreover, the junction of the edge of the opening and the hood forms an angle over seventy degrees, and results in a great power loss of the air at the angle. Hence the suction at two sides of the opening is much lower. In short, the aforesaid problems make suction airflow strength uneven in the hood, and result in a portion of the dust cannot be drawn into the air discharge duct and scatter outside the hood. Not only the power of the inhalation device connected to the air discharge duct is wasted, it also creates a lot of energy waste.